(1) Field of the Invention
This invention relates to a technique for applying protective tape to a wafer surface with a pattern formed thereon and for separating the protective tape from the wafer surface.
(2) Description of the Related Art
In a conventional process of manufacturing semiconductor wafers, a mechanical method such as grinding or polishing, or a chemical method including etching, is used to process the back surfaces of semiconductor wafers (hereinafter simply called xe2x80x9cwafersxe2x80x9d) to reduce the thickness thereof. When these methods are used to process the wafers, a protective tape is applied to the front surfaces of wafers in order to protect the front surfaces having wiring patterns formed thereon.
When a wafer is sent to a back-grinding process, the front surface (patterned surface) is suction-supported by a chuck table and the back surface is ground with a grinder. At this time, a protective tape is applied to the front surface to avoid the pattern being damaged under the stress of grinding occurring to the front surface, and to avoid contamination of the pattern.
The wafer thinned by grinding of its back surface could easily be broken during the processing or transportation. The wafer, due to its deflection or bending, is difficult to handle. In order to avoid such inconveniences, a proposal has been made to apply two different types of protective tape to a wafer surface beforehand to prevent damage and bending of the wafer (see Japanese Patent Publication (Unexamined) 2000-331968).
The use of protective tape in double plies as described in the above Japanese Patent Publication (Unexamined) 2000-331968 has an advantage in terms of wafer reinforcement, but has the following inconveniences encountered in the process of applying and separating the protective tape.
Generally when protective tape is applied to the surface of a wafer, an applicator roller is made to roll and press on the protective tape for applying it to the surface of the wafer while the protective tape is stretched in a direction of application. However, when applying the protective tape in two plies to the surface of a wafer as in the prior art, it is difficult to stretch the protective tape by means of the applicator roller because the protective tape itself is greater in rigidity than a single piece of tape. The stress generated at this point and acting on the wafer could damage the wafer.
Further, when separating the protective tape in two plies all at once, the high rigidity of the tape allows only an unsharp folding angle as the tape is folded for separation from the wafer. As a result, a strong pulling force is required to separate the protective tape. This strong pulling force acting on the thinned wafer could damage the wafer.
Further, when the protective tape applied in two plies to the wafer surface is cut along the periphery of the wafer, the thickness and rigidity encumber the cutting operation.
This invention has been made having regard to the state of the art noted above, and its primary object is to provide protective tape applying and separating methods capable of easily applying and separating protective tape to/from semiconductor wafers while reinforcing the wafers by giving rigidity thereto.
The above object is fulfilled, according to this invention, by a method of applying protective tapes to a surface of a semiconductor wafer with a pattern formed thereon, the method comprising a step of applying the protective tapes to the surface of the wafer by repeating a process of applying each of the protective tapes.
With the protective tape applying method according to this invention, individual protective tapes are applied to the surface of a wafer in a repeated operation, to facilitate handling, e.g. applying and cutting, of the protective tapes. That is, this method allows a protective tape of low rigidity to be handled as a unit, rather than handling a highly rigid protective tape formed in two plies in advance. Thus, the wafer is subjected to a reduced stress due to pressing and stretching of the protective tape during application of the protective tape. Only a single protective tape has to be cut along the wafer, which is easier than cutting a plurality of protective tapes at a time. An existing apparatus may be used to repeat the process of applying an individual protective tape to the surface of the wafer, without requiring special protective tape or apparatus. Thus, an apparatus for executing this method may be constructed at low cost.
In this invention, the protective tapes applied in a plurality of plies to the surface of the wafer, preferably, are progressively harder upward away from the surface.
A soft protective tape is directly applied to the patterned surface to absorb irregularities on the surface of the patterned surface, thereby rendering the surface level and smooth. Thus, a second and subsequent protective tapes may be applied substantially uniformly to the flat surface of the protective tape forming the under layer.
Further, it is preferred in this invention that the protective tapes applied in a plurality of plies to the surface of the wafer comprise a UV curable tape applied to the surface of the wafer, and a non-TV curable tape applied to the UV curable tape.
A UV irradiation of the UV curable tape applied to the surface of the wafer will reduce the adhesive strength of the tape. Thus, the protective tape may easily be separated from the surface of the wafer.
Further, it is preferable to apply each of the protective tapes in a different direction. For example, the protective tapes may be applied such that, after a first protective tape is applied to the surface of the wafer in a first direction, a next protective tape is applied in a direction perpendicular to the first direction.
By varying the direction for applying the protective tapes, the tension of the protective tapes is uniformly applied to the wafer. This is effective to correct a warp of the thinned wafer.
In another aspect of the invention, a method is provided for separating a plurality of protective tapes applied to a surface of a semiconductor wafer with a pattern formed thereon. This tape method comprises a step of individually separating the plurality of protective tapes in plural times starting with an uppermost tape.
With the protective tape separating method according to this invention, protective tapes applied in a plurality of plies to the surface of a wafer are separated one by one starting with an uppermost tape. Thus, the protective tapes may be separated with a relatively small pulling force. This reduces the stress due to the pulling force acting on the thinned wafer. The protective tapes may be separated easily from the surface of the wafer.
Preferably, the plurality of protective tapes are separated such that, after a first protective tape is separated in a first direction, a next protective tape is separated in a direction perpendicular to the first direction. Alternatively, the plurality of protective tapes may be separated by varying separating directions in accordance with the pattern on the surface.
Particularly, by separating the protective tapes along recesses in the patterned surface, the protective tapes may be separated efficiently without leaving an adhesive lodged in the recesses.